Google, Facebook and Twitter's decision to establish their European bases in Dublin has opened the internet giants up to EU defamation and privacy laws like never before, a libel lawyer has warned.

The world's biggest search engine and the social networks' presence in Ireland will also enable lawyers to sue the companies on behalf of clients abused by anonymous bloggers and tweeters according to Paul Tweed, the Belfast-based libel expert.

Tweed, who has acted in libel cases for Jennifer Lopez, Harrison Ford and recently The X Factor judge Louis Walsh, who accepted damages €500,000 (£421,000) from the Sun, said it will be the likes of Google, Twitter and Facebook who will pay the ultimate price for the "abusive, anonymous blogger in his underpants".

He added that his law firm, Johnsons, has recently sent warning letters and emails to individual bloggers and tweeters who have abused journalists and politicians. Johnsons has also sent warnings to the relevant internet servers providers.

"We will send a 'take down' notice to either Google, Facebook or Twitter and we get various responses. Two or three years ago our demands for 'take down' notices were largely ignored by the likes of Google who are based in Seattle and could quote us back the American constitution," Tweed said.

"In those days we used to tell our clients 'look, even if we get a judgment we are not going to be able to enforce it'. Because US courts would not enforce them and our clients basically had to turn the other cheek.

"Now the whole landscape has changed. The massive game-changer is that the likes of Facebook, Twitter and Google have established European headquarters in Dublin and in doing that they have subjected themselves not only to Irish defamation and privacy laws but also those EU laws on libel and privacy. That means they are potentially a target because they are providing anonymous abusers on line with a platform."

The libel lawyer revealed that about 60% of the cases he is currently dealing with are connected to the online abuse and alleged defamation of his clients. The majority of the clients are Irish and British journalists, Tweed added, although he would not disclose any names.

"There is a big, big problem here with regard to online abuse and libel because once the privacy horse is bolted you can't put it back in the stable," he said. "In the past a newspaper like the News of the World, when it printed defamatory material about a client, could be forced to print an apology that was proportionate to the damage done to that client. With online this defamatory and often threatening material is passed on within seconds around the world. Once it's out there it's out there for good somewhere."

Tweed denied that he is seeking to curb internet freedom and insisted that he was creating a "deterrent" to those who use social media and other online outlets to spread fear and falsehoods about individuals.

"I love newspapers and I admire real journalists. They put their names to stories and stand up to be counted if they get it wrong. These guys blogging away in their underpants in their mammy's attic spreading lies about people – some of them dedicated, hard-working journalists whom I know personally – have to be held accountable somehow," he said.

"These guys in anoraks are the playground bullies of the internet and the only way to deter them is to make the platforms they use accountable. If these internet behemoths are not held accountable for the actions of these abusers, law, and I would argue genuine journalism, will collapse."

• To contact the MediaGuardian news desk email editor@mediaguardian.co.uk or phone 020 3353 3857. For all other inquiries please call the main Guardian switchboard on 020 3353 2000. If you are writing a comment for publication, please mark clearly "for publication".

• To get the latest media news to your desktop or mobile, follow MediaGuardian on Twitter and Facebook.